the roslagsbanan commuter rail is the only actively used 2 ft 11 ^3^โ32 in railway in the world.
...honestly, with a wikipedia article that extensive it hardly qualifies as "obscure".
so, bonus:
the siljan area of sweden has a history of building observation towers:
the tower in the black-and-white photo, which started this trend, was financed by a man who made a fortune making and selling multiplication books. basically like books of logarithm tables but only for multiplication. 1ร1 to 9999ร9999.
also that entire area is europe's largest meteorite crater:
